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Bilge Dweller
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Joined: Sat Jun 03, 2017 11:47 am
Currently located: India


Postby mann84 » Tue Jun 27, 2017 11:14 am

Quantity of lub oil for medium speed engine is less, about 500 litre remaining on-board. There is no convenient port nearby where we can take bunker. Can I use 2 stroke main engine crankcase oil in 4 stroke medium speed engine.Main engine crankcase oil is Total Lubmarine Atlanta Marine D3005, SAE30 , TBN 5 oil. Medium speed engine oil is Total Lubmarine Aureli XL 4040, SAE40, TBN 30 oil.

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D Winsor
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Joined: Thu Nov 22, 2007 8:23 am
Currently located: Dartmouth


Postby D Winsor » Tue Jun 27, 2017 12:05 pm

Yes you probably can but it should be a last resort move and only used to "Top Up" the existing oil charge. I would also recommend operating the 4 stroke engines on diesel fuel if they are currently set burn heavy fuel.

I don't believe there will be an issue with blending of the 2 lubricants considering both are from the same supplier and possibly base stock

The 2 stroke engine oil is however of a lower viscosity and does not have the detergent additives so you will most likely experience a drop in oil pressure and an increased risk of clogged oil filters and or purifiers due to oil contamination from combustion gasses.

I would also recommend ordering a sufficient supply of the lubricating oil required for the 4 stoke engines to do a complete change of the 2 stroke engine oil contaminated oil charge in any engine the 2 stroke engine oil had been added
Troubleshooting 101 "Don't over think it - K.I.S.S. it"

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Big Pete
Engineering Mentor
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Joined: Fri Apr 24, 2009 11:18 pm
Currently located: Solihull, England


Postby Big Pete » Wed Jun 28, 2017 9:38 am

As D. Winsor says, you should get away with it but order enough of the correct oil to do a full oil change and change all the oil filters at the same.

The Detergents in the 4 stroke oil keeps soot and other Dirt particles in suspension in the oil and stops sludge accumulating on the engine parts, so when you go back to Detergent oil you can expect a lot of sludge deposits to lift off and be dumped in the filters and you may have to change them more frequently for a while. It might be possible to "improve" the TBN and detergency of the oil by adding some cylinder lube into the Blend, but that might cause more problems than it would solve.

The lower viscosity could cause a drop in oil pressure, however, the oil pump should be designed to deliver more than enough oil to maintain the pressure on the engine, even when it is badly worn, the surplus oil is dumped back into the Sump through a spring loaded relief valve to maintain the correct oil pressure, so that should compensate for some of the pressure drop, you could increase the viscosity of the oil by lowering the temperature, that should help maintain the oil pressure and increase the viscous drag on the shafts and hence improve the hydro dynamic wedge lubrication, which is more important in avoiding metal to metal contact than the oil pressure.

Another thing to consider is the densities of the two grades will be different, if a large amount of 2 stroke oil is added you may have problems with the purifiers and have to change the Gravity Discs.
However, you obviously have internet/ email access so why not discus this with your oil supplier for confirmation? It will at least give you some peace of mind over this problem.

One old Polish Fitter than I sailed with many years ago was on a Polish Baltic Ferry that had a major oil leak on its main engine, lost the whole oil charge, so they filled the sump with liquid detergent from a road tanker they were carrying as cargo and used that in the main engine until they got back into Port. Must have been a nice clean engine afterwards!!

Good Luck and let us know how you got on.
It is always better to ask a stupid question than to do a stupid thing.

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